The present invention relates to an electrostatic actuator for driving a slider or a movable section with an electrostatic force and a method of driving the same, particularly, to an electrostatic actuator having an improved simple structure and capable of driving the slider or the movable section with a high accuracy and a method of driving the same.
The electrostatic actuator for driving a slider or a movable section has already been disclosed in some publications, e.g., Japanese Patent Disclosure (Kokai) No. 8-140367, and xe2x80x9cElectrostatic Linear Microactuator Mechanism, JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. 17, No. 1, Jan. 1999, IEEExe2x80x9d. The actuator disclosed in these publications comprises an array of electrodes as shown in FIG. 1. In this electrostatic actuator, a slider or a movable section 102 is arranged slidable forward as denoted by an arrow 101 or backward between two stators 103A and 103B arranged to face each other. An electrode section 104 is provided on the slider 102. Two systems of stator electrodes 106A and 106C to which voltage is applied at different timings are alternately arranged on the stator 103A. Likewise, two systems of electrodes 106B and 106D to which voltage is applied at different timings are arranged on the other stator 103B. The electrodes 106A to 106D provided on the stators 103A, 103B and the electrode section 104 of the slider 102 are substantially equal to each other in the pitch and the electrode width. Also, the electrodes 106A, 106C of the stator 103A and the electrodes 106B, 106D of the stator 103B are arranged such that the phase of the arrangement is shifted by xc2xd.
If a voltage is applied from a voltage source (not shown) to the electrode 106A in the electrostatic actuator of the particular construction, an electrostatic force, i.e., Coulomb force, is generated between the electrode 106A and the electrode section 104, with the result that the slider 102 is attracted toward the stator 103A such that the electrode 106A and the electrode section 104 are allowed to faced to each other. Then, when the switching circuit (not shown) for supplying a voltage is switched-to change the electrode to which a voltage is supplied from the electrode 106A to the electrode 106B so as to supply a voltage to the electrode 106B, the slider 102 is attracted toward the other stator 103B such that the electrodes 106B and the electrode section 104 are allowed to faced to each other. Also, when the switching circuit is switched to change the electrode to which a voltage is supplied from the electrode 106B to the electrode 106C so as to supply a voltage to the electrode 106C, the slider 102 is attracted toward the stator 103A again such that the electrodes 106C and the electrode section 104 are allowed to faced to each other. Further, when the switching circuit is switched to change the electrode to which a voltage is supplied from the electrode 106C to the electrode 106D so as to supply a voltage to the electrode 106D, the slider 102 is attracted toward the stator 103B again such that the electrodes 106D and the electrode section 104 are allowed to faced to each other. As described above, if a voltage is applied successively to the electrodes 106A, 106B, 106C and 106D, the slider 102 is vibrated microscopically between the stators 103A and 103B and is macroscopically driven in the forward direction as denoted by the arrow 101 in FIG. 1. If the order of applying a voltage to the electrodes is reversed such that the voltage is applied to the electrodes 106D, 106C, 106B and 106A in the order mentioned, the slider 102 is driven in the backward direction opposite to the forward direction denoted by the arrow 101 in FIG. 1.
In the electrostatic actuator described above, it is necessary for the pair of stators 103A and 103B to be aligned with a high accuracy. It is also necessary for the electrodes of the same width to be formed equidistantly with a high accuracy in the stators 103A, 103B. Naturally, a sufficient time and labor are required for manufacturing the parts of the electrostatic actuator and for assembling these parts with a high accuracy, leading to a high manufacturing cost of the actuator. This problem of the high manufacturing cost must be overcome for realizing a mass production of the actuator.
A method of applying voltage and the operating principle of the conventional electrostatic actuator will now be described with reference to FIG. 1. Incidentally, those members of the actuator, which are substantially same as those shown in FIG. 1 are denoted by the same reference numerals in FIG. 2 for avoiding the overlapping description.
As described above with reference to FIG. 1, if a voltage is applied successively to the electrodes 106A to 106D provided on the stators 103A and 103B, the slider 102 is driven so as realize a linear movement on a macroscopic level. In the electrostatic actuator shown in FIG. 2, the electrodes 106A and 106B are covered with a dielectric film 105 so as to prevent these electrodes 106A, 106B from the insulation breakdown, as disclosed in Japanese Patent Disclosure No. 8-140367 referred to previously.
If a voltage is applied first to the electrode 106A as shown in FIG. 2, dielectric polarization 107 is generated in a dielectric film 105 covering the electrode 106A. Then, if a voltage is applied to the electrode 106B, the slider 102 is attracted toward the other stator 103B so as to be driven such that the electrode section 104 is allowed to face the electrode 106B. It should be noted, however, that the component of the dielectric polarization generated in the dielectric film 105 mounted on the electrode 106A produces the function of keeping the slider 102 attracted toward the stator 103A. The component of the force produced by the dielectric polarization 107 is very small in terms of the potential level. However, since the distance between the stator 103A and the electrode section 104 of the slider 102 is short, it is possible for the force generated by the dielectric polarization 107 not to be negligible as a force for inhibiting the movement of the slider 102. This is based on the fact that the electrostatic force is inversely proportional to the square of the distance between the electrodes. Under the circumstances, the driving of the slider 102 tends to be unstable in the conventional electrostatic actuator. It should also be noted that the degree of the charge leakage in the dielectric film 105, i.e., the time for the dielectric polarization to disappear, is not constant, which also provides a cause of the failure for the movement of the slider 102 to be made constant.
As described above, in the conventional electrostatic actuator, it is necessary to align accurately the two stators 103A and 103B so as to provide accurately a desired phase of arrangement of these two stators. It is also necessary to form accurately the electrodes facing the two surfaces of the slider or movable element 102. It follows that a long time and much labor are required for assembling the actuator, leading to a high manufacturing cost. In other words, serious problems must be solved before the mass production of the actuator is realized.
It should also be noted that, in the conventional electrostatic actuator, the driving operation of the slider 102 tends to become unstable because of the influence produced by the dielectric polarization taking place in the dielectric film covering the electrode.
What should also be noted is that the degree of the charge leakage in the dielectric film 105, i.e., the time for the dielectric polarization to disappear, is not constant, which also provides a cause of the failure for the movement of the slider 102 to be made constant.
An object of the present invention is to provide an electrostatic actuator, which permits improving the assembling efficiency and the mass production capability and also permits the slider to make a stable microscopic movement with a relatively high accuracy.
According to a first aspect of the present invention, there is provided an electrostatic actuator mechanism, comprising:
a first stator provided with an electrode group including at least three electrodes successively arranged in a predetermined direction, voltage being applied to the electrodes in different order;
a second stator arranged to face the first stator and provided with a planar electrode extending in the predetermined direction;
a movable member arranged between the first stator and the second stator, and provided with a first electrode section facing the electrode group and a second electrode section facing the planar electrode; and
a switching circuit configured to apply voltage alternately to the electrode group and the planar electrode, the potential of any of the electrodes forming the electrode group being rendered higher than the potential of the first electrode section, or the potential of the planar electrode being rendered higher than the potential of the second electrode section, and to switch the order of applying voltage successively to the first electrode group.
It is possible for the electrostatic actuator of the present invention to further comprise a dielectric film formed to cover the electrode group.
It is also possible for the electrostatic actuator of the present invention to further a dielectric film formed to cover the first electrode section.
Further, where the dielectric film is formed, it is possible for the electrostatic actuator of the present invention to further comprise a circuit configured to impair a potential difference such that the potential of the electrode group is rendered lower than the potential of the first electrode section, when voltage is applied to the planar electrode.
It is possible for that the slider having a surface which is perpendicular to the predetermined direction to form an optical element surface.
It is possible for the first and second stators to have stoppers projecting from the upper surfaces of the electrode group and the planar electrode, and for the movable member to be provided with regions in which the stoppers are slid, the region being formed on the surfaces on which the first and second electrode sections are formed.
Also, it is possible for the movable member to have stoppers projecting from the surfaces of the first and second electrode sections, and for the first and second stators to be provided with regions in which the stoppers are slid, the regions being formed on the surfaces on which the electrode group and the planar electrode are formed.
Further, it is possible for the first stator to include a first part and for the second stator to include a second part, the first and second parts being connected to each other to form a stator.
According to a second aspect of the present invention, there is provided a method of driving an electrostatic actuator mechanism including a first stator having an electrode group including at least three electrodes successively arranged in a predetermined direction, voltage being applied to the electrodes in different order, a second stator arranged to face the first stator and having a planar electrode extending in the predetermined direction, and a movable member arranged between the first stator and the second stator and having a first electrode section facing the electrode group and a second electrode section facing the planar electrode, the method comprising:
applying voltage to the electrode group, the potential of any of the electrodes forming the electrode group being rendered higher than the potential of the first electrode section;
applying voltage to the planar electrode, the potential of the planar electrode being rendered higher than that of the second electrode section;
applying voltage by switching the electrode of the first electrode group such that the potential of the switched electrode is rendered higher than the potential of first electrode section;
applying voltage such that the potential of the planar electrode is rendered higher than the potential of the second electrode section; and
repeating the voltage application defined above.
Further, according to a third embodiment of the present invention, there is provided a camera module, comprising:
a image pick-up element; and
an electrostatic actuator mechanism mounted to the image pick-up element, the electrostatic actuator mechanism including;
a first stator provided with an electrode group including at least three electrodes successively arranged in a predetermined direction, voltage being applied to the electrodes in different order,
a second stator arranged to face the first stator and provided with a planar second electrode extending in the predetermined direction,
a movable member arranged between the first stator and the second stator, and provided with a first electrode section facing the electrode group, a second electrode section facing the planar electrode, and an optical element configured to form an optical image on the image pick-up element, and
a switching circuit configured to apply voltage alternately to the electrode group and the planar electrode, the potential of any of the electrodes forming the electrode group being rendered higher than the potential of the first electrode section, or the potential of the planar electrode being rendered higher than the potential of the second electrode section, and to switch the order of applying voltage successively to the electrode group.